Lipid Cubic Phase for Membrane Protein X-ray Crystallography

Abstract

Membrane proteins constitute an integral part of biomembrane and play key roles in fundamental biological and physiological processes such as metabolism, signaling, and ion homeostasis. About half of all drug targets are membrane proteins. Elucidation of three-dimensional structures of membrane proteins by X-ray crystallography can provide mechanistic insights for their cellular activity and reveal atomic resolution of architectural details for rational design of novel therapeutics. However, the pace of IMP crystallography has been relatively slow due to great challenges in crystallization. Lipid cubic phase (LCP) has proven to be promising in tackling the crystallization problem by providing a membrane-alike environment. Its bilayer is composed of neutral lipids, such as monoacylglycerols, and can accommodate a substantial amount of native lipids such as phospholipids and cholesterol. Thus, the structure and composition of LCP mimic biomembranes and therefore offer a native-like environment for membrane proteins, which is favorable for functionality and crystallization. Here, the principles for LCP formation, membrane protein reconstitution, and crystallization process are described. The successful application of LCP crystallization for a wide range of membrane proteins including receptors, complexes, transporters, channels, enzymes, membrane protein insertion chaperons, and outer membrane β-barrels is summarized. General methods and protocols for this method are also described.

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Acknowledgements

This work was supported by the 1000 Young Talent Program, the Shanghai Pujiang Talent Program (15PJ1409400), the National Natural Science Foundation of China (No. 31570748 and U1632127), the CAS Shanghai Science Research Center (CAS-SSRC-YJ-2015-02), and Key Program of CAS Frontier Science (QYZDB-SSW-SMC037).